Gas alarm circuit



Nov, 30, 1965 TOKIHIKO YONEDA GAS ALARM CIRCUIT Filed March 9, 1962 6%.(0 HM M United States Patent Ofitice 3,221,320 Patented Nov. 30, 19653,221,320 GAS ALARM CIRCUIT Toirihiiro Yoneda, Charo-kn, Tokyo-to,Japan, assignor to Komyo Rilragaku Kogyo Kabushilri Kaisha, Tokyo-to,Japan, a joint=stock company of Japan Filed Mar. 9, 1962, Ser. No.178,743 Claims priority, application Japan, Apr. 13, 1961, Bic/12,648 4Claims. (Cl. 340-237) The present invention relates to gas alarm systemsand more particularly to a gas alarm system which has no mechanicalcomponents or moving mechanical parts.

In a conventional gas alarm system, the. output of the gas concentrationdetecting circuit is led to a meter relay and let out as an ON-OFFoutput, or this output is led through a pre-amplifier to a relay and ledout as an alarm output. The operational flow sequences in these casesare as follows:

Detecting circuit output- Meter relay- Amplifier- Power relay- Alarm;

Detecting circuit output- Amplifier Relay Power relay- Alarm;

Since several stages of mechanical switching elements and a preamplifierare indispensable, the apparatus becomes large and it has been extremelyditficult to maintain operational stability over long periods of time.

It is an object of the present invention to provide a new gas alarmsystem circuit of simple arrangement which does not require apreamplifier and a large number of mechanical switching elements, andwhich can be operated with stability over long periods of time.

Another object of the present invention is to provide a circuit asabove-stated which has a relatively low power consumption, is easilyadjusted, and has a wide range of practical applications.

Said objects and other objects of the present invention have beenattained by a gas alarm arrangement comprising a hot-wire type gasconcentration detection circuit including a variable resistance, anoscillation circuit coupled to the output of said detection circuitwhich is preset, by a bias potential imposed thereon by controlledregulation of the said variable resistance, to oscillate when the outputof the detection circuit reaches a predetermined value. A couplingcircuit which is connected to the oscillation circuit couples theoscillating circuit to an amplifier the output of which activates anaudio alarm device, so that, when the oscillating circuit oscillates,the oscillation is amplified at a desired audio frequency to be emittedat a desired intensity in a audible manner.

The nature and details of the invention as well as the manner in whichthe afore-stated objects may best be achieved will be more clearlyapparent by reference to the following description of one representativeembodiment of the invention when taken in conjunction with theaccompanying drawing, which is an electrical circuit diagram of acircuit embodying the invention.

The input side of the embodiment illustrated consists of a gasconcentration detection circuit a which is a bridge circuit comprisingan exposed detecting hot wire F 2. compensating hot wire F fixedresistors R R and a variable resistor VR for alarm giving. The hot wiresF and F have an equal electrical resistance and are made of platinum thesurfaces of which have been activated and caused to have extremely highcatalytic efficiency. The compensating hot wire F is hermetically sealedwithin a container containing pure air. The out put side of the circuita is connected in series with an oscillating circuit D which includes atunnel diode and an LC coupling circuit consisting of a capacitor C andan inductance coil L Coil L in turn is coupled to an inductance coil Lof an amplifier b, the output of which is impressed on a loudspeaker SP.The amplifier 12 com prises a condenser C resistors R R transistors T Tand T and an output transformer OT. In this embodiment, a common powersupply is used for the circuits a and b.

The above-described arrangement operates as follows: The exposeddetecting hot wire F is exposed to an atmosphere of the gas to bedetected, and the compensating hot wire F is preheated by an electriccurrent to the same temperature as the hot wire F The output of the gasconcentration detection circuit a is then obtained as a function of theratio of the resistance (which is a function of the gas concentration)of the hot wire F to the resistance of the hot wire F The alarm point isset by regulating the output potential of the detecting circuit by meansof the variable resistor VR. When the gas is detected and the output ofthe circuit a cancels the bias due to the variable resistor VR and hasreached a value corresponding to the peak voltage of the diodescharacteristic immediately prior to its unstable region, oscillationoccurs at the instant of transition of the oscillating element D to itsunstable region. This oscillation, the frequency of which may beregulated to a desired audio frequency by suitably selecting the coil Land capacitor C of the coupling circuit, is then amplified by theamplifier b and caused to activate the loudspeaker SP, whereby an alarmis sounded.

Since, in the gas alarm circuit of the present invention, the variableresistance for circuit balancing is utilized additionally as aresistance for regulating the oscillation point of the alarm oscillationcircuit, that is, for setting the alarm, the composition of the circuitis extremely simple and is easily adjusted. Accordingly, this circuitmay be used for a wide range of applications. For example, it may beused to detect continuously the concentration of an explosive gas andsound an alarm when the said concentration reaches the lower explosivelimit of the said gas, or it may be used continuously to detect theoccurrence of leakage of a noxious gas and sound an alarm when such aleakage occurs.

Moreover, by the utilization of an oscillation element in the manneraccording to this invention, it is possible to obtain a continuousoutput variation of the gas concentration detection circuit, directly,as a switching oscillation output, without the use of any mechanicalconversion medium. Therefore, it is possible to manufacture a gas alarmsystem which is substantially more compact than a conventional system ofsimilar type, and which, moreover, consumes only a low rate of power.

Although this invention has been described with respect to a particularembodiment thereof, it is not to be so limited as changes andmodifications may be made therein which are within the full intendedscope of the invention, as defined by the appended claims.

What is claimed is: 1. A gas alarm arrangement, comprising incombination;

a gas detection circuit providing an output having a predetermined valueupon detecting a particular gas;

an oscillation circuit coupled to said detection circuit, including onits input side a semiconductor diode having a negative resistance regionand accomplishing a switching operation upon receiving an input over thepeak point thereof, said diode passing current upon receiving an inputexceeding said peak point, said oscillation circuit supplying a signalin response to the action of said diode;

amplifying means coupled to the output of said oscillation circuitreceiving and amplifying said signal; and

alarm giving means responsive to said amplifying means 4. lation circuitreceiving and amplifying said signal; and alarm giving means responsiveto said amplifying means providing an alarm in response to saidamplified providing an alarm in response to said amplified 5 signal.signal. 4. A gas alarm arrangement, comprising in combina- 2. A gasalarm arrangement, comprising in combination; tion; a bridge-type gasdetection circuit providing an output a gas detection circuit providingan output having a signal having a predetermined value upon detecting apredetermined value upon detecting a particular particular gas includingan exposed hot Wire, a gas; shielded Wire, first and second resistors tobalance an oscillation circuit including a semiconductor diode saidWires and an adjustable bias resistor for fine on the input side thereofcoupled to said detection balancing; circuit, said diode having anegative resistance-region an oscillation circuit including, asemiconductor diode and accomplishing a switching operation uponreresponsive to the bridge-type gas detection circuit ceiving an inputover a. peak point'thereof, a tank on the input side of said oscillationcircuit coupled circuit including an inductance coil and capacitor tosaiddetection circuit, said diode only passing curconnected in parallel,said tank circuit being in series rent upon receiving an input having atleast said with said diode supplying a signal in response to thepredetermined value, a tank circuit including an action of said diode;inductance coil and capacitor in series with said amplifying meanscoupled to the output of said oscildiode supplying a signal in responseto the action lation circuit receiving and, amplifying said signal; ofsaid diode; and, amplifying means coupled to the output of saidoscilalarm giving means'responsive to said amplifying means lationcircuit receiving and amplifying said signal;

providing an alarm in responseto said amplified 23 and signal. alarmgiving means responsive to said amplifying 3. A gas alarm arrangement,comprisingiin combinameans providing an alarm in response to saidamtion; plified signal.

a gas detection circuit. providing an output having a predeterminedvalue upon detecting a particular References Cited by the Examiner gasincluding a bridge circuit having a' variable re- UNITED STATES PATENTSsistor adapted to balance said circuit, said circuit biasing a potentialreaching a peak point of a diode g 9/1946 Chatterlea et a1 331 107 inthe next circuit stage; g 9/1957 Strange 73 27 an oscillation circuit asthe next circuit stage, coupled gg gggg t g 33 to said detection circuitand including a semiconduc- 013149 12/1961 H 3 tor diode balanced bysaid variable resistor, conarase nected to said bridge circuit so thatsaid diode passes FOREIGN PATENTS an output signal when the, biaspotential preset by 113 867 9/1941 Australia.

said bridge circuit is canceled: by the output signal of. 835:933 5/1960Great Britain the detecting circuit and the peak pointof the diode isexceeded, a tank circuit including an inductance OTHER REFERENCES Coiland capacitor Connected in Parallel, Said tank IBM Technical DisclosureBulletin; Light Powered circuit being in Series with Said diode pp y aOscillator by Miller; vol. 3, No. 4, September 1960. signal in responseto the action of said diode;

amplifying means coupled to the output of said oscil- NEIL C. READ,Primary Examiner.

1. A GAS ALARM ARRANGEMENT, COMPRISING IN COMBINATION; A GAS DETECTIONCIRCUIT PROVIDING AN OUTPUT HAVING A PREDETERMINED VALUE UPON DETECTINGA PARTICULAR GAS; AN OSCILLATION CIRCUIT COUPLED TO SAID DETECTIONCIRCUIT, INCLUDING ON ITS INPUT SIDE A SEMICONDUCTOR DIODE HAVING ANEGATIVE RESISTANCE REGION AND ACCOMPLISHING A SWITCHING OPERATION UPONRECEIVING AN INPUT OVER THE PEAK POINT THEREOF, SAID DIODE PASSINGCURRENT UPON RECEIVING AN INPUT EXCEEDING SAID PEAK POINT, SAIDOSCILLATION CIRCUIT SUPPLY A SIGNAL IN RESPONSE TO THE ACTION OF SAIDDIODE; AMPLIFYING MEANS COUPLED TO THE OUTPUT OF SAID OSCILLATIONCIRCUIT RECEIVING AND AMPLIFYING SAID SIGNAL; AND ALARM GIVING MEANSRESPONSIVE TO SAID AMPLIFYING MEANS PROVIDING AN ALARM IN RESPONSE TOSAID AMPLIFIED SIGNAL.